A thought (well, half of one at least):
One thing that occurs to me regarding the "it doesn't hurt until I notice it" issue, for children in particular, is that when they "hurt themselves" (for want of a better phrase), for example when falling off a swing, they will seek for cues suggesting how to react.
If no-one's watching they may just get back on the swing and carry on; if a friend's there they may laugh it off; if mummy's there they may cry (I strongly suspect that adults do something similar ). The response to the stimulus certainly appears to be dependent on social and emotional context.
This is nowhere near an explanation of course - kids don't suddenly cease to feel pain when mummy leaves the room (I would guess, anyway) - but it may go some way to explaining the development of a perception of "pain" as a socially-mediated response.
Alternatively, the kid in the above example may actually feel "pain" in all 3 of the situations, but their reaction to that "pain" is different (i.e. socially-mediated).
I'm losing it - but then I said it was only half a thought! It's way too early for me to be thinking...need glucose and caffeine
